/*
 * Copyright (c) JForum Team
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met:
 * 
 * 1) Redistributions of source code must retain the above 
 * copyright notice, this list of conditions and the 
 * following  disclaimer.
 * 2)  Redistributions in binary form must reproduce the 
 * above copyright notice, this list of conditions and 
 * the following disclaimer in the documentation and/or 
 * other materials provided with the distribution.
 * 3) Neither the name of "Rafael Steil" nor 
 * the names of its contributors may be used to endorse 
 * or promote products derived from this software without 
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT 
 * HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, 
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
 * THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER 
 * IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE
 * 
 * This file creation date: 25/08/2004 23:03:14
 * The JForum Project
 * http://www.jforum.net
 */
package net.jforum;

import java.sql.Connection;

import net.jforum.util.preferences.ConfigKeys;
import net.jforum.util.preferences.SystemGlobals;

import org.apache.log4j.Logger;

/**
 * Base class for all database connection implementations that may be used with
 * JForum. Default implementations are <code>PooledConnection</code>, which is
 * the defeault connection pool implementation, and
 * <code>SimpleConnection</code>, which opens a new connection on every request.
 * 
 * @author Rafael Steil
 * @version $Id: DBConnection.java,v 1.14 2006/08/23 02:24:06 rafaelsteil Exp $
 */
public abstract class DBConnection {
    private static final Logger logger = Logger.getLogger(DBConnection.class);
    protected boolean isDatabaseUp;

    private static DBConnection instance;

    /**
     * Creates an instance of some <code>DBConnection </code>implementation.
     * 
     * @return <code>true</code> if the instance was successfully created, or
     *         <code>false</code> if some exception was thrown.
     */
    public static boolean createInstance() {
	try {
	    instance = (DBConnection) Class
		    .forName(
			    SystemGlobals
				    .getValue(ConfigKeys.DATABASE_CONNECTION_IMPLEMENTATION))
		    .newInstance();
	} catch (Exception e) {
	    logger.warn("Error creating the database connection implementation instance. "
		    + e);
	    e.printStackTrace();
	    return false;
	}

	return true;
    }

    /**
     * Gets the current <code>DBConnection</code> implementation's instance
     * 
     * @return DBConnection
     */
    public static DBConnection getImplementation() {
	return instance;
    }

    /**
     * Checks if database connection is up.
     * 
     * @return <code>true</code> if a connection to the database was
     *         successfully created, or <code>false</code> if not.
     */
    public boolean isDatabaseUp() {
	return this.isDatabaseUp;
    }

    /**
     * Inits the implementation. Connection pools may use this method to init
     * the connections from the database, while non-pooled implementation can
     * provide an empty method block if no other initialization is necessary. <br>
     * Please note that this method will be called just once, at system startup.
     * 
     * @throws Exception
     */
    public abstract void init() throws Exception;

    /**
     * Gets a connection. Connection pools' normal behaviour will be to once
     * connection from the pool, while non-pooled implementations will want to
     * go to the database and get the connection in time the method is called.
     * 
     * @return Connection
     */
    public abstract Connection getConnection();

    /**
     * Releases a connection. Connection pools will want to put the connection
     * back to the pool list, while non-pooled implementations should call
     * <code>close()</code> directly in the connection object.
     * 
     * @param conn
     *            The connection to release
     */
    public abstract void releaseConnection(Connection conn);

    /**
     * Close all open connections.
     * 
     * @throws Exception
     */
    public abstract void realReleaseAllConnections() throws Exception;
}
